JPS6046030B2 - Print head manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a printhead used in a printer.

Thin film thermal printheads with resistive heater elements are also described in detail in, for example, US Pat. No. 3,609,294.

In this printhead, a planar resistive heater element is covered by a thermally conductive and electrically resistive overcoat. This protective film is formed as a raised area on each heater element. These raised mesa-like areas are simply thicker portions of the coating that protects the entire substrate. Heat is concentrated in the mesa-shaped region, and is applied to a heat-sensitive recording medium placed close to the mesa-shaped region. However, since the recording medium is selected to have a high thermal conductivity, some of the heat generated by the resistive heater element and conducted to the surface of the recording medium is transferred to the thinner parts of the coating. It gets transmitted and wasted. The thermal efficiency of this system is therefore necessarily low. In the present invention, a resistive element is formed on a mesa-shaped region formed by a glass glaze layer.

This mesa-shaped area places the heat source itself in close proximity to the heat-sensitive recording medium, reducing heat dissipated through the protective film. Therefore, the thermal efficiency of the present invention is extremely improved. U.S. Pat. No. 3,598 for barriers to ion migration.
It is introduced in issue 956.

This barrier to ion migration consists of a conductive shield, which prevents ions from entering the resistive heater element and reduces the life of the heater element. This barrier to prevent ion migration is isolated from the resistive heater element and the heat-sensitive recording medium by a glass layer, and is most effective when electrically biased or grounded. be. The barrier for preventing ion migration according to the present invention functions without electrical bias or ground, and does not require a separating layer of glass between the barrier and the resistive heater element.

Furthermore, the barrier according to the invention enhances the adhesion between the resistive heater element and the anti-wear layer. The barrier described above is formed during a heat treatment step to adjust the resistance of the resistive heater element.

By controlling the temperature and time of the heat treatment, the resistance value is increased to a resistance value that is compatible with the electronic circuit in which the heater element is used. Thin film technology allows resistive material to be deposited more uniformly than other processes, so external trimming resistors are not required. Since the heat treatment affects the resistance values of all heater elements uniformly, the resistance values of the heater elements can be adjusted in an increasing direction to suit the electronic circuit. FIG. 1 is a cross-sectional view of a substrate with a glass glaze layer used for manufacturing a reprint head according to the invention, shown at an early stage of manufacture. ing.

The glass glaze layer has a mesa-shaped region formed for each heater element. In the figure, a substrate 10 is coated with a thick layer of high temperature glass glaze layer 12. The glass glaze layer 12 is then coated with photoresist, baked, exposed and! Development is performed. As a result, a pattern of photoresist is left where it is desired to create mesa-like areas. The exposed glaze layer is then etched with hydrofluoric acid to a thickness thinner than the mesa region 14. Here, the substrate 10 is, for example, 94% to 994% aluminum oxide or its equivalent. After a mesa-like region is formed for each resistive heater element as shown in FIG.
A coating of resistive material is applied over the entire glass glaze layer by thin film techniques such as vapor deposition or sputtering. A layer of conductive material is then formed over the same area using similar thin film techniques. In embodiments of the invention, the resistive material is either tantalum nitride or an alloy of tantalum and aluminum or equivalents thereof. and said conductive material is either gold or aluminum or an equivalent thereof. FIG. 2 is a cross-sectional view of a structure in which layers of a resistive material and a conductive material are formed on the substrate shown in FIG. 1, and is shown in the process of being manufactured.

In the figure, resistive material 20 is formed over mesa-like region 14 . A photoresist is applied onto the conductive material 22, baked, exposed and developed to form a pattern of conductors for powering the heater elements. The conductive material 22 is then chemically etched to form a respective electrical conductor to each resistive heater element. Since the resistive material 20 in the areas between the conductors must be removed, the material in those areas is removed by a suitable etching process or similar process. Thereafter, photoresist is again applied over the entire area except where a resistive heater element is to be formed on the mesa-shaped area 14. This defines the portion of the resistive heater element. After baking, exposing and developing, conductive material 22 is etched away from the top of resistive material 20 covering mesa-like region 14. Prior to forming the anti-wear layer on the heater element, the entire substrate is heat treated.

Figure 3 shows time (minutes) on the horizontal axis and resistance change rate (%) on the vertical axis.
) is a diagram showing the time-resistance change rate characteristics of tantalum nitride with temperature as a parameter.

As shown in the figure, by controlling the temperature and time of the heat treatment, the amount of change in resistance value of each resistive heater element is controlled. Since the resistance change is essentially constant for all resistive heater elements on the board, this heat treatment changes the resistance of the heater element to suit the particular electronic circuit in which it is used. It can be adjusted in the direction of increase.
During the heat treatment, a protective oxide layer is formed over each resistive heater element. This protective oxide layer acts as a barrier to ion migration from commonly known ion sources such as heat-sensitive recording media. Ions that travel to and enter heater elements contaminate these heater elements. As a result, the reliability of the device is reduced and the life of the device is shortened. Furthermore, this protective oxide layer provides better adhesion of the anti-wear layer to each heater element after heat treatment. FIG. 4 is a cross-sectional view of a printhead made in accordance with the present invention with a protective oxide layer and an anti-wear layer.

In the figure, an anti-wear layer 30 is formed on top of each heater element. The material of the anti-wear layer is a wear-resistant, thermally conductive material such as aluminum oxide. A resistive heater element is thus constructed which is formed on the glass glaze layer, forms a barrier to ion migration, and is protected by an anti-wear layer. This resistive heater element enables effective printing on a heat-sensitive recording medium. The area 34 shown in FIG. 4 is where the resistive heater element is printed. By using the protective oxide layer 32, reliability is improved by about 6 times in an environment where ions are generated. For example, according to experiments, about 90007T1. When printing on the above paper, there were six times as many heater element malfunctions when the protective oxide layer 32 was not present as compared to when the protective oxide layer was present. FIG. 5 shows a diagram constructed in accordance with one embodiment of the present invention. 1 is a plan view of a printhead having multiple heater elements; FIG.

As shown, a thin film thermal printhead 40 includes, for example, seven resistive heater elements 41, a common conductor 42, and a separate conductor 44. Each resistive heater element 41 and its associated electrical conductor 44 are formed as described above. The print head 40 is used as a printer head for printing a 5×7 matrix of alphanumeric characters in a printer, which is also detailed in the specification of JP-A No. 59641 filed by the present applicant. can be used.

[Brief explanation of the drawing]

1 is a cross-sectional view of a substrate with a glass glaze layer used for manufacturing a reprint head according to the invention; FIG.
The figure is a cross-sectional view of a structure in which layers of resistive and conductive materials are formed on the substrate shown in Figure 1, and Figure 3 shows the relationship between time and resistance change of tantalum nitride using temperature as a parameter. FIG. 4 is a cross-sectional view of a print head manufactured according to the present invention, and FIG. 5 is a top view of a print head manufactured according to the present invention. 10: Substrate, 12: Glass glaze layer, 14: Mesa-shaped region, 20: Resistive material, 22: Electric conductor, 30: Anti-wear layer, 32: Protective oxide layer, 40: Thermal print head, 4
1: heater element, 42: common conductor, 44: conductor.

Claims (1)

[Claims] 1 Forming a glass glaze layer partially having a mesa-like region on an aluminum oxide substrate, then forming a resistive material layer at least on the mesa-like region to form a resistive heater element, and then forming a conductive material layer on the resistive material layer and removing a portion of the conductive material layer corresponding to the resistive material layer portion covering the mesa-shaped region; heat treating the layer of material to form a resistive protective oxide layer on the portion of the resistive material layer overlying the mesa-like region, and then overlying at least the resistive protective oxide layer to prevent abrasion; forming a layer, controlling the temperature and time of heat treatment of the resistive material layer to set the resistance value of the resistive material layer to a desired resistance value, and controlling the resistive protective oxide layer during the heat treatment. A method for manufacturing a print head, characterized in that a print head is formed simultaneously.